A rocker arm for an engine sways in response to a rotation motion of a cam, and opens and closes an intake valve and an exhaust valve. In order to reduce a friction loss during the above operation, the following technique is conventionally well known, that is, while an outer ring provided between a pair of leg parts of the rocker arm is rotatably supported by a cageless type roller bearing, the rocker arm and the cam are in rolling contact with each other.
While the cageless type roller bearing can be used under a high-load condition, an outer ring end face and a roller end face come into contact with a leg part of the rocker arm and could bite it. Especially, when the rocker arm is made of light metal, the rocker arm is excessively abraded. In addition, the roller bearing is damaged by metal powder generated due to the abrasion.
Thus, with a view to eliminating the abrasion of the rocker arm, well-known roller bearings are disclosed in Utility Model Registration No. 2508561 (Patent document 1), Utility Model Registration No. 2508562 (Patent document 2), and Utility Model Publication No. 6-25606 (Patent document 3).
Each of the roller bearings disclosed in the patent documents 1 to 3 is provided to prevent the rocker arm from being abraded in such a manner that a plate is arranged between the rocker arm and a roller end face.